Aircraft quality epoxy, S-2 glass, etc

Every year as the season starts I read where folks talk about how such-and-such a board is stronger/stiffer/better because of the use of a specific resin or fabric.

I like to do this test as an example of demonstration that resin and fiber, while important, have less impact than the construction and thickness of the board in determining final stiffness.

This is a picture of some crappy 1 pound Lowes insulation that is 1" thick and about 1.5" wide. It's suspended between two containers and I can get about 40 oz of weight on it before it get dangerously close to breaking.

The vast majority of wakesurfers are a sandwich construction. That is it's foam sandwiched between two layers of fiberglass. There are composite sandwich boards that have high density foam skins or wood laminates and may also have layers of glass on the outside and inside of the skin.

For purposes of demonstration, I am going to just create a sandwich from copier paper and elmers white glue. Definately not aircraft grade epoxy or S-2 'glass.

After my sandwich "cured" it is able to withstand an increase in weight of approximately 1500% and remain in the same field of deflection.

There is some interpolation because I couldn't get the weights to balance AND take a picture

In the construction of a sandwich, whenever you glue three things together the plane where they are all resisting the force makes that area extraordinarily stiff, regardless of the resin textile making up the sandwich.

Additionally, a greater amount of stiffness can be imparted to the sandwich by increasing the distance between the skins. That is the thicker the board for a given weight, construction etc, the stiffer that board will be.

I love working with paper and glue!

Finally!!! Some materials I can work with! I'm gonna start making my first "paper board" tonight!

Oh, wait...

Too funny - I was noticing that this was my BEST lamination EVER.

The distribution on the weight is significantly different on the second picture. Your demonstration and point are however good.

Paper boards? Sounds like on of my projects.

Yeah. In the minutes precceding that picture, which was about 5:30 am, all of those cans fell on the floor. Judy entered the kitchen asking if everything was OK. Seeing that I was playing with epoxy and foam, she had her answer

I just couldn't get the stupid cans to standup, so not scientific, however, I trust the point was clear. That being: don't let your cans hit the floor at 5:30 AM.

Long before the Middle Ages and the ponderous catapults they used, the ancient Greeks used bow catapults that could shoot more weight about 3 times as far. Alexander the Great used them with great success in conquering most of the world.
The bows were multilayer composites designed to take the flex and stress loads. Sadly paper and carbon mat were not available, but they had other carbon based composites.
They used bone on the inside due to its great compressive strength. Wood in the center to provide the maximum spring and leather on the outside because it had good tension properties.
We get to reinvent a great deal as the world goes on, but more to the point is that a little examination of what happens can generate new ways of looking at things.

Probably you could have left out the upper paper lamination and had almost the same strength due to the lack of compressive strength in paper. However the combination of glue and paper on the upper surface might have stopped some of the distortion in the foam the the compression caused and stiffened it more than expected.

You always have cool stuff to contemplate Jeff.

Art, are you an engineer or just a walking dictionary? Your post's are usually very informative.

There are four engineers in my immediate family, three more that are in-laws and I'm the only one that actually builds stuff. But I'm not an engineer, I took marketing. I kind of learn by osmosis so I gain some knowledge on things that catch my quirky interest.
My wife will tell you that I don't always know what I'm talking about . (But I'm pretty careful to be accurate, and I'll always admit when I'm wrong).

Jeff might actually build a crossbow. I would not likely get around to it. That's why he's more interesting.

(Message edited by rallyart on April 09, 2009)

Yeah! I'm more interesting! Everyone knows baldING CPA's are the most interesting folks ever. Thanks for the props Art...but you aren't going to be sending me a bill are you?

"Probably you could have left out the upper paper lamination and had almost the same strength due to the lack of compressive strength in paper."

Strength and stiffness, in this demo, are two different things, as I'm sure you're aware. The ability of the crappy EPS foam to move creates shear and so adds "strength" if not stifffness.

Interesting enough, copier paper seems to be junk in both compression and tension but the side under compression (deck) adds significantly to the overall stiffness of the sandwich. I'm really not sure how much the Elmer's adds to the equation. I've witnessed the same thing with playing cards. If I super-glue two of them together, it's still pretty "flexy" but add a third and there is a significant increase in rigidity.

From my rudimentary and NOT scientific experiments, stiffness is impacted, in a declining order by:

1) Sandwich composition
2) Distance between the skins (thicker board)
3) Stiffness of the core material
4) Skin facing material, assuming copier paper isn't an option
5) Resin matrix

While I'm at it, I've noticed some continuing confusion with construction. There are two basic construction methods in use for wakesurfers today. They revolve around the foam that is being used - polyurethane and EPS. Often times folks will ERRONEOUSLY refer to the one construction as fiberglass and the other as epoxy.

MOSTLY Fiberglass is used in BOTH constructions, the only thing that differs is the foam and the resin that is used. EPS melts with exposure to the styrenes in polyester resin which was the mainstay for polyurethane board building for years. The one notable exception is Carbon. Texalium is still fiberglass with aluminum powder on one side.

So when the underlying foam is EPS, the resin will be Epoxy. The correct terminology would be Polyurethane/Polyester (often shortened to PuPe) and EPS/Epoxy.

Further, "Epoxy" boards do contain a fabric in the resin matrix, almost always fiberglass. While epoxy will remain resiliant longer than polyester, it is still a very soft plastic and by itself won't keep foam stiff enough to ride on. In terms of both resins, fiberglass is what gives the resin strength and stiffness.

So...the term "Fiberglass" is not a distinguishing characteristic of the differnce in construction, but IS an identifier of someone that doesn't understand the construction.

Spot on SD.
"
Better to keep you mouth shut and let them think you are a fool the open and remove all doubt"

Is there anyone out there that has tried to use a paper product to construct boards? Could you replace a layer of fiberglass with a layer of paper to reduce the cost of a board? I ask the question because paper can be recycled, and is sometimes virtually free!

JON T

Show did! I couldn't seem to find his build thread in the archive, for the first board that was skinned with shopping bags. I think that Roy made a board with contact paper skin.

This build, of Ed's, has cardboard and rice paper throughout.

http://www.wakeworld.com/MB/Discus/messages/559019/516714.html

Hopefully, Ed will check in and describe his 427 pound recycled shopping bag board.

Nice, that is a pretty intense build by Ed. A ton of work, but who said building wakesurf boards was easy!

now, now , i thought it was 25#

I wouldn't recommend paper or cardboard. I made the Pizza Hut and Kroger’s boards just to see if I could do it. I did run in to Tom Morey on MySpace. Tom gets credit for making the first cardboard surfboard and for organizing the first surfing competitions. Ever hear of a Morey Boogie board, I have one.

http://www.wakeworld.com/MB/Discus/messages/559019/393481.html
http://www.wakeworld.com/MB/Discus/messages/559019/396194.html
http://www.wakeworld.com/MB/Discus/messages/559019/399231.html

Hmmmm... The Kroger’s board is closer to 25 pounds.

25 #'s,, not to bad!! Thanks for the post, it was interesting to see all the work you put into that board. Good learning curve on that one.

Jon T